Protocol documentation: Difference between revisions
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This page ''describes'' the behavior of the [[Original Bitcoin client|reference client]]. The Bitcoin protocol is specified by the behavior of the reference client, not by this page. In particular, while this page is quite complete in describing the [[network]] protocol, it does not attempt to list all of the rules for block or transaction validity. | |||
Type names used in this documentation are from the C99 standard. | Type names used in this documentation are from the C99 standard. | ||
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''d7'' is the Merkle root of the 3 transactions in this block. | ''d7'' is the Merkle root of the 3 transactions in this block. | ||
Note: Hashes in Merkle Tree displayed in the [[Block Explorer]] are of little-endian notation. For some implementations and [http://www.fileformat.info/tool/hash.htm calculations], the | Note: Hashes in Merkle Tree displayed in the [[Block Explorer]] are of little-endian notation. For some implementations and [http://www.fileformat.info/tool/hash.htm calculations], the bytes need to be reversed before they are hashed, and again after the hashing operation. | ||
=== Signatures === | === Signatures === | ||
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Bitcoin uses [http://en.wikipedia.org/wiki/Elliptic_curve_cryptography Elliptic Curve] [http://en.wikipedia.org/wiki/Digital_Signature_Algorithm Digital Signature Algorithm] ([http://en.wikipedia.org/wiki/Elliptic_Curve_DSA ECDSA]) to sign transactions. | Bitcoin uses [http://en.wikipedia.org/wiki/Elliptic_curve_cryptography Elliptic Curve] [http://en.wikipedia.org/wiki/Digital_Signature_Algorithm Digital Signature Algorithm] ([http://en.wikipedia.org/wiki/Elliptic_Curve_DSA ECDSA]) to sign transactions. | ||
For ECDSA the secp256k1 curve from http://www.secg.org/ | For [[ECDSA]] the secp256k1 curve from http://www.secg.org/sec2-v2.pdf is used. | ||
Public keys (in scripts) are given as 04 <x> <y> where ''x'' and ''y'' are 32 byte big-endian integers representing the coordinates of a point on the curve or in compressed form given as <sign> <x> where <sign> is 0x02 if ''y'' is even and 0x03 if ''y'' is odd. | Public keys (in scripts) are given as 04 <x> <y> where ''x'' and ''y'' are 32 byte big-endian integers representing the coordinates of a point on the curve or in compressed form given as <sign> <x> where <sign> is 0x02 if ''y'' is even and 0x03 if ''y'' is odd. | ||
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Each ''input'' must have a cryptographic digital signature that unlocks the funds from the prior transaction. Only the person possessing the appropriate [[private key]] is able to create a satisfactory signature; this in effect ensures that funds can only be spent by their owners. | Each ''input'' must have a cryptographic digital signature that unlocks the funds from the prior transaction. Only the person possessing the appropriate [[private key]] is able to create a satisfactory signature; this in effect ensures that funds can only be spent by their owners. | ||
Each ''output'' determines which Bitcoin address (or other criteria, see [[ | Each ''output'' determines which Bitcoin address (or other criteria, see [[Script]]) is the recipient of the funds. | ||
In a transaction, the sum of all inputs must be equal to or greater than the sum of all outputs. If the inputs exceed the outputs, the difference is considered a [[transaction fee]], and is redeemable by whoever first includes the transaction into the block chain. | In a transaction, the sum of all inputs must be equal to or greater than the sum of all outputs. If the inputs exceed the outputs, the difference is considered a [[transaction fee]], and is redeemable by whoever first includes the transaction into the block chain. | ||
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== Common structures == | == Common structures == | ||
Almost all integers are encoded in little endian. Only IP or port number are encoded big endian. | Almost all integers are encoded in little endian. Only IP or port number are encoded big endian. All field sizes are numbers of bytes. | ||
=== Message structure === | === Message structure === | ||
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| main || 0xD9B4BEF9 || F9 BE B4 D9 | | main || 0xD9B4BEF9 || F9 BE B4 D9 | ||
|- | |- | ||
| testnet || 0xDAB5BFFA || FA BF B5 DA | | testnet/regtest || 0xDAB5BFFA || FA BF B5 DA | ||
|- | |- | ||
| testnet3 || 0x0709110B || 0B 11 09 07 | | testnet3 || 0x0709110B || 0B 11 09 07 | ||
|- | |||
| signet(default) || 0x40CF030A || 0A 03 CF 40 | |||
|- | |- | ||
| namecoin || 0xFEB4BEF9 || F9 BE B4 FE | | namecoin || 0xFEB4BEF9 || F9 BE B4 FE | ||
Line 136: | Line 137: | ||
! Value !! Storage length !! Format | ! Value !! Storage length !! Format | ||
|- | |- | ||
| < | | < 0xFD || 1 || uint8_t | ||
|- | |- | ||
| <= | | <= 0xFFFF || 3 || 0xFD followed by the length as uint16_t | ||
|- | |- | ||
| <= | | <= 0xFFFF FFFF || 5 || 0xFE followed by the length as uint32_t | ||
|- | |- | ||
| - || 9 || | | - || 9 || 0xFF followed by the length as uint64_t | ||
|} | |} | ||
If you're reading the Satoshi client code (BitcoinQT) it refers to this as a "CompactSize". Modern | If you're reading the Satoshi client code (BitcoinQT) it refers to this encoding as a "CompactSize". Modern Bitcoin Core also has the VARINT macro which implements an even more compact integer for the purpose of local storage (which is incompatible with "CompactSize" described here). VARINT is not a part of the protocol. | ||
=== Variable length string === | === Variable length string === | ||
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! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| | | 1+ || length || [[Protocol_documentation#Variable_length_integer|var_int]] || Length of the string | ||
|- | |- | ||
| ? || string || char[] || The string itself (can be empty) | | ? || string || char[] || The string itself (can be empty) | ||
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=== Network address === | === Network address === | ||
When a network address is needed somewhere, this structure is used | When a network address is needed somewhere, this structure is used. Network addresses are not prefixed with a timestamp in the version message. | ||
{|class="wikitable" | {|class="wikitable" | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| 4 || time || uint32 || the Time (version >= 31402) | | 4 || time || uint32 || the Time (version >= 31402). '''Not present in version message.''' | ||
|- | |- | ||
| 8 || services || uint64_t || same service(s) listed in [[#version|version]] | | 8 || services || uint64_t || same service(s) listed in [[#version|version]] | ||
|- | |- | ||
| 16 || IPv6/4 || char[16] || IPv6 address. Network byte order. The original client only | | 16 || IPv6/4 || char[16] || IPv6 address. Network byte order. The original client only supported IPv4 and only read the last 4 bytes to get the IPv4 address. However, the IPv4 address is written into the message as a 16 byte [http://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresses IPv4-mapped IPv6 address] | ||
(12 bytes ''00 00 00 00 00 00 00 00 00 00 FF FF'', followed by the 4 bytes of the IPv4 address). | (12 bytes ''00 00 00 00 00 00 00 00 00 00 FF FF'', followed by the 4 bytes of the IPv4 address). | ||
|- | |- | ||
Line 213: | Line 214: | ||
|- | |- | ||
| 2 || MSG_BLOCK || Hash is related to a data block | | 2 || MSG_BLOCK || Hash is related to a data block | ||
|- | |||
| 3 || MSG_FILTERED_BLOCK || Hash of a block header; identical to MSG_BLOCK. Only to be used in getdata message. Indicates the reply should be a merkleblock message rather than a block message; this only works if a bloom filter has been set. See BIP 37 for more info. | |||
|- | |||
| 4 || MSG_CMPCT_BLOCK || Hash of a block header; identical to MSG_BLOCK. Only to be used in getdata message. Indicates the reply should be a cmpctblock message. See BIP 152 for more info. | |||
|- | |||
| 0x40000001 || MSG_WITNESS_TX || Hash of a transaction with witness data. See BIP 144 for more info. | |||
|- | |||
| 0x40000002 || MSG_WITNESS_BLOCK || Hash of a block with witness data. See BIP 144 for more info. | |||
|- | |||
| 0x40000003 || MSG_FILTERED_WITNESS_BLOCK || Hash of a block with witness data. Only to be used in getdata message. Indicates the reply should be a merkleblock message rather than a block message; this only works if a bloom filter has been set. See BIP 144 for more info. | |||
|} | |} | ||
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! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| 4 || version || | | 4 || version || int32_t || Block version information (note, this is signed) | ||
|- | |- | ||
| 32 || prev_block || char[32] || The hash value of the previous block this particular block references | | 32 || prev_block || char[32] || The hash value of the previous block this particular block references | ||
Line 230: | Line 241: | ||
| 32 || merkle_root || char[32] || The reference to a Merkle tree collection which is a hash of all transactions related to this block | | 32 || merkle_root || char[32] || The reference to a Merkle tree collection which is a hash of all transactions related to this block | ||
|- | |- | ||
| 4 || timestamp || uint32_t || A timestamp recording when this block was created (Will overflow in 2106<ref> | | 4 || timestamp || uint32_t || A timestamp recording when this block was created (Will overflow in 2106<ref>https://en.wikipedia.org/wiki/Unix_time#Notable_events_in_Unix_time</ref>) | ||
|- | |- | ||
| 4 || bits || uint32_t || The calculated difficulty target being used for this block | | 4 || bits || uint32_t || The calculated difficulty target being used for this block | ||
Line 236: | Line 247: | ||
| 4 || nonce || uint32_t || The nonce used to generate this block… to allow variations of the header and compute different hashes | | 4 || nonce || uint32_t || The nonce used to generate this block… to allow variations of the header and compute different hashes | ||
|- | |- | ||
| 1 || txn_count || [[ | | 1+ || txn_count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of transaction entries, this value is always 0 | ||
|} | |||
cf. [[Block hashing algorithm]] | |||
=== Differential encoding === | |||
Several uses of CompactSize below are "differentially encoded". For these, instead of using raw indexes, the number encoded is the difference between the current index and the previous index, minus one. For example, a first index of 0 implies a real index of 0, a second index of 0 thereafter refers to a real index of 1, etc. | |||
=== PrefilledTransaction === | |||
A PrefilledTransaction structure is used in HeaderAndShortIDs to provide a list of a few transactions explicitly. | |||
{|class="wikitable" | |||
! Field Name !! Type !! Size !! Encoding || Purpose | |||
|- | |||
| index || [[Protocol_documentation#Variable_length_integer|CompactSize]] || 1, 3 bytes || Compact Size, differentially encoded since the last PrefilledTransaction in a list || The index into the block at which this transaction is | |||
|- | |||
| tx || Transaction || variable || As encoded in [[Protocol_documentation#tx|tx messages]] || The transaction which is in the block at index index. | |||
|} | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== HeaderAndShortIDs === | |||
A HeaderAndShortIDs structure is used to relay a block header, the short transactions IDs used for matching already-available transactions, and a select few transactions which we expect a peer may be missing. | |||
{|class="wikitable" | |||
! Field Name !! Type !! Size !! Encoding || Purpose | |||
|- | |||
| header || Block header || 80 bytes || First 80 bytes of the block as defined by the encoding used by "block" messages || The header of the block being provided | |||
|- | |||
| nonce || uint64_t || 8 bytes || Little Endian || A nonce for use in short transaction ID calculations | |||
|- | |||
| shortids_length || [[Protocol_documentation#Variable_length_integer|CompactSize]] || 1 or 3 bytes || As used to encode array lengths elsewhere || The number of short transaction IDs in shortids (ie block tx count - prefilledtxn_length) | |||
|- | |||
| shortids || List of 6-byte integers || 6*shortids_length bytes || Little Endian || The [[Protocol_documentation#Short_transaction_ID|short transaction IDs]] calculated from the transactions which were not provided explicitly in prefilledtxn | |||
|- | |||
| prefilledtxn_length || [[Protocol_documentation#Variable_length_integer|CompactSize]] || 1 or 3 bytes || As used to encode array lengths elsewhere || The number of prefilled transactions in prefilledtxn (ie block tx count - shortids_length) | |||
|- | |||
| prefilledtxn || List of PrefilledTransactions || variable size*prefilledtxn_length || As defined by [[Protocol_documentation#PrefilledTransaction|PrefilledTransaction]] definition, above || Used to provide the coinbase transaction and a select few which we expect a peer may be missing | |||
|} | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== BlockTransactionsRequest === | |||
A BlockTransactionsRequest structure is used to list transaction indexes in a block being requested. | |||
{|class="wikitable" | |||
! Field Name !! Type !! Size !! Encoding || Purpose | |||
|- | |||
| blockhash || Binary blob || 32 bytes || The output from a double-SHA256 of the block header, as used elsewhere || The blockhash of the block which the transactions being requested are in | |||
|- | |||
| indexes_length || [[Protocol_documentation#Variable_length_integer|CompactSize]] || 1 or 3 bytes || As used to encode array lengths elsewhere || The number of transactions being requested | |||
|- | |||
| indexes || List of [[Protocol_documentation#Variable_length_integer|CompactSizes]] || 1 or 3 bytes*indexes_length || [[Protocol_documentation#Differential_encoding|Differentially encoded]] || The indexes of the transactions being requested in the block | |||
|} | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== BlockTransactions === | |||
A BlockTransactions structure is used to provide some of the transactions in a block, as requested. | |||
{|class="wikitable" | |||
! Field Name !! Type !! Size !! Encoding || Purpose | |||
|- | |||
| blockhash || Binary blob || 32 bytes || The output from a double-SHA256 of the block header, as used elsewhere || The blockhash of the block which the transactions being provided are in | |||
|- | |||
| transactions_length || [[Protocol_documentation#Variable_length_integer|CompactSize]] || 1 or 3 bytes || As used to encode array lengths elsewhere || The number of transactions provided | |||
|- | |||
| transactions || List of Transactions || variable || As encoded in [[Protocol_documentation#tx|tx messages]] || The transactions provided | |||
|} | |} | ||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== Short transaction ID === | |||
Short transaction IDs are used to represent a transaction without sending a full 256-bit hash. They are calculated by: | |||
# single-SHA256 hashing the block header with the nonce appended (in little-endian) | |||
# Running SipHash-2-4 with the input being the transaction ID and the keys (k0/k1) set to the first two little-endian 64-bit integers from the above hash, respectively. | |||
# Dropping the 2 most significant bytes from the SipHash output to make it 6 bytes. | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
== Message types == | == Message types == | ||
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| 8 || timestamp || int64_t || standard UNIX timestamp in seconds | | 8 || timestamp || int64_t || standard UNIX timestamp in seconds | ||
|- | |- | ||
| 26 || addr_recv || net_addr || The network address of the node receiving this message | | 26 || addr_recv || [[#Network address|net_addr]] || The network address of the node receiving this message | ||
|- | |- | ||
|colspan="4"| version | |colspan="4"| Fields below require version ≥ 106 | ||
|- | |- | ||
| 26 || addr_from || net_addr || | | 26 || addr_from || [[#Network address|net_addr]] || Field can be ignored. This used to be the network address of the node emitting this message, but most P2P implementations send 26 dummy bytes. The "services" field of the address would also be redundant with the second field of the version message. | ||
|- | |- | ||
| 8 || nonce || uint64_t || Node random nonce, randomly generated every time a version packet is sent. This nonce is used to detect connections to self. | | 8 || nonce || uint64_t || Node random nonce, randomly generated every time a version packet is sent. This nonce is used to detect connections to self. | ||
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| 4 || start_height || int32_t || The last block received by the emitting node | | 4 || start_height || int32_t || The last block received by the emitting node | ||
|- | |- | ||
| 1 || relay || bool || Whether the remote peer should announce relayed transactions or not, see [https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki BIP 0037] | |colspan="4"| Fields below require version ≥ 70001 | ||
|- | |||
| 1 || relay || bool || Whether the remote peer should announce relayed transactions or not, see [https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki BIP 0037] | |||
|} | |} | ||
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|- | |- | ||
| 1 || NODE_NETWORK || This node can be asked for full blocks instead of just headers. | | 1 || NODE_NETWORK || This node can be asked for full blocks instead of just headers. | ||
|- | |||
| 2 || NODE_GETUTXO || See [https://github.com/bitcoin/bips/blob/master/bip-0064.mediawiki BIP 0064] | |||
|- | |||
| 4 || NODE_BLOOM || See [https://github.com/bitcoin/bips/blob/master/bip-0111.mediawiki BIP 0111] | |||
|- | |||
| 8 || NODE_WITNESS || See [https://github.com/bitcoin/bips/blob/master/bip-0144.mediawiki BIP 0144] | |||
|- | |||
| 16 || NODE_XTHIN || Never formally proposed (as a BIP), and discontinued. Was historically sporadically seen on the network. | |||
|- | |||
| 64 || NODE_COMPACT_FILTERS || See [https://github.com/bitcoin/bips/blob/master/bip-0157.mediawiki BIP 0157] | |||
|- | |||
| 1024 || NODE_NETWORK_LIMITED || See [https://github.com/bitcoin/bips/blob/master/bip-0159.mediawiki BIP 0159] | |||
|} | |} | ||
Hexdump example of version message (OBSOLETE EXAMPLE | Hexdump example of version message (OBSOLETE EXAMPLE: This example lacks a checksum and user-agent): | ||
<pre> | <pre> | ||
0000 F9 BE B4 D9 76 65 72 73 69 6F 6E 00 00 00 00 00 ....version..... | 0000 F9 BE B4 D9 76 65 72 73 69 6F 6E 00 00 00 00 00 ....version..... | ||
Line 328: | Line 436: | ||
76 65 72 73 69 6F 6E 00 00 00 00 00 - "version" command | 76 65 72 73 69 6F 6E 00 00 00 00 00 - "version" command | ||
64 00 00 00 - Payload is 100 bytes long | 64 00 00 00 - Payload is 100 bytes long | ||
35 8d 49 32 - payload checksum (internal byte order) | |||
Version message: | Version message: | ||
Line 343: | Line 451: | ||
=== verack === | === verack === | ||
The ''verack'' message is sent in reply to ''version''. This message consists of only a [[#Message structure|message header]] with the command string "verack". | The ''verack'' message is sent in reply to ''[[#version|version]]''. This message consists of only a [[#Message structure|message header]] with the command string "verack". | ||
Hexdump of the verack message: | Hexdump of the verack message: | ||
Line 355: | Line 463: | ||
76 65 72 61 63 6B 00 00 00 00 00 00 - "verack" command | 76 65 72 61 63 6B 00 00 00 00 00 00 - "verack" command | ||
00 00 00 00 - Payload is 0 bytes long | 00 00 00 00 - Payload is 0 bytes long | ||
5D F6 E0 E2 - Checksum | 5D F6 E0 E2 - Checksum (internal byte order) | ||
</pre> | </pre> | ||
Line 366: | Line 474: | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| 1+ || count || [[ | | 1+ || count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of address entries (max: 1000) | ||
|- | |- | ||
| 30x? || addr_list || (uint32_t + net_addr)[] || Address of other nodes on the network. version < 209 will only read the first one. The uint32_t is a timestamp (see note below). | | 30x? || addr_list || (uint32_t + [[#Network address|net_addr]])[] || Address of other nodes on the network. version < 209 will only read the first one. The uint32_t is a timestamp (see note below). | ||
|} | |} | ||
Line 384: | Line 492: | ||
61 64 64 72 00 00 00 00 00 00 00 00 - "addr" | 61 64 64 72 00 00 00 00 00 00 00 00 - "addr" | ||
1F 00 00 00 - payload is 31 bytes long | 1F 00 00 00 - payload is 31 bytes long | ||
ED 52 39 9B - checksum | ED 52 39 9B - payload checksum (internal byte order) | ||
Payload: | Payload: | ||
Line 400: | Line 508: | ||
Allows a node to advertise its knowledge of one or more objects. It can be received unsolicited, or in reply to ''getblocks''. | Allows a node to advertise its knowledge of one or more objects. It can be received unsolicited, or in reply to ''getblocks''. | ||
Payload (maximum | Payload (maximum 50,000 entries, which is just over 1.8 megabytes): | ||
{|class="wikitable" | {|class="wikitable" | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| | | 1+ || count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of inventory entries | ||
|- | |- | ||
| 36x? || inventory || [[Protocol specification#Inventory Vectors|inv_vect]][] || Inventory vectors | | 36x? || inventory || [[Protocol specification#Inventory Vectors|inv_vect]][] || Inventory vectors | ||
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getdata is used in response to inv, to retrieve the content of a specific object, and is usually sent after receiving an ''inv'' packet, after filtering known elements. It can be used to retrieve transactions, but only if they are in the memory pool or relay set - arbitrary access to transactions in the chain is not allowed to avoid having clients start to depend on nodes having full transaction indexes (which modern nodes do not). | getdata is used in response to inv, to retrieve the content of a specific object, and is usually sent after receiving an ''inv'' packet, after filtering known elements. It can be used to retrieve transactions, but only if they are in the memory pool or relay set - arbitrary access to transactions in the chain is not allowed to avoid having clients start to depend on nodes having full transaction indexes (which modern nodes do not). | ||
Payload (maximum | Payload (maximum 50,000 entries, which is just over 1.8 megabytes): | ||
{|class="wikitable" | {|class="wikitable" | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| | | 1+ || count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of inventory entries | ||
|- | |- | ||
| 36x? || inventory || [[Protocol specification#Inventory Vectors|inv_vect]][] || Inventory vectors | | 36x? || inventory || [[Protocol specification#Inventory Vectors|inv_vect]][] || Inventory vectors | ||
Line 431: | Line 539: | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| | | 1+ || count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of inventory entries | ||
|- | |- | ||
| 36x? || inventory || [[Protocol specification#Inventory Vectors|inv_vect]][] || Inventory vectors | | 36x? || inventory || [[Protocol specification#Inventory Vectors|inv_vect]][] || Inventory vectors | ||
Line 442: | Line 550: | ||
The locator hashes are processed by a node in the order as they appear in the message. If a block hash is found in the node's main chain, the list of its children is returned back via the ''inv'' message and the remaining locators are ignored, no matter if the requested limit was reached, or not. | The locator hashes are processed by a node in the order as they appear in the message. If a block hash is found in the node's main chain, the list of its children is returned back via the ''inv'' message and the remaining locators are ignored, no matter if the requested limit was reached, or not. | ||
To receive the next blocks hashes, one needs to issue getblocks again with a new block locator object. Keep in mind that some clients | To receive the next blocks hashes, one needs to issue getblocks again with a new block locator object. Keep in mind that some clients may provide blocks which are invalid if the block locator object contains a hash on the invalid branch. | ||
Payload: | Payload: | ||
Line 451: | Line 559: | ||
| 4 || version || uint32_t || the protocol version | | 4 || version || uint32_t || the protocol version | ||
|- | |- | ||
| 1+ || hash count || [[ | | 1+ || hash count || [[Protocol_documentation#Variable_length_integer|var_int]] || number of block locator hash entries | ||
|- | |- | ||
| 32+ || block locator hashes || char[32] || block locator object; newest back to genesis block (dense to start, but then sparse) | | 32+ || block locator hashes || char[32] || block locator object; newest back to genesis block (dense to start, but then sparse) | ||
Line 462: | Line 570: | ||
<pre> | <pre> | ||
// From libbitcoin which is under AGPL | // From libbitcoin which is under AGPL | ||
std::vector<size_t> | std::vector<size_t> block_locator_indexes(size_t top_height) | ||
{ | { | ||
std::vector<size_t> indexes; | |||
std::vector<size_t> | |||
// | // Modify the step in the iteration. | ||
int64_t step = 1; | |||
for ( | |||
// Start at the top of the chain and work backwards. | |||
for (auto index = (int64_t)top_height; index > 0; index -= step) | |||
{ | { | ||
if ( | // Push top 10 indexes first, then back off exponentially. | ||
if (indexes.size() >= 10) | |||
step *= 2; | step *= 2; | ||
indexes.push_back((size_t)index); | |||
} | } | ||
return | // Push the genesis block index. | ||
indexes.push_back(0); | |||
return indexes; | |||
} | } | ||
</pre> | </pre> | ||
Line 483: | Line 597: | ||
=== getheaders === | === getheaders === | ||
Return a ''headers'' packet containing the headers of blocks starting right after the last known hash in the block locator object, up to hash_stop or 2000 blocks, whichever comes first. To receive the next block headers, one needs to issue getheaders again with a new block locator object | Return a ''headers'' packet containing the headers of blocks starting right after the last known hash in the block locator object, up to hash_stop or 2000 blocks, whichever comes first. To receive the next block headers, one needs to issue getheaders again with a new block locator object. Keep in mind that some clients may provide headers of blocks which are invalid if the block locator object contains a hash on the invalid branch. | ||
Payload: | Payload: | ||
Line 492: | Line 606: | ||
| 4 || version || uint32_t || the protocol version | | 4 || version || uint32_t || the protocol version | ||
|- | |- | ||
| 1+ || hash count || [[ | | 1+ || hash count || [[Protocol_documentation#Variable_length_integer|var_int]] || number of block locator hash entries | ||
|- | |- | ||
| 32+ || block locator hashes || char[32] || block locator object; newest back to genesis block (dense to start, but then sparse) | | 32+ || block locator hashes || char[32] || block locator object; newest back to genesis block (dense to start, but then sparse) | ||
Line 499: | Line 613: | ||
|} | |} | ||
For the block locator object in this packet, the same rules apply as for the [[ | For the block locator object in this packet, the same rules apply as for the [[Protocol_documentation#getblocks|getblocks]] packet. | ||
=== tx === | === tx === | ||
''tx'' describes a bitcoin transaction, in reply to ''getdata'' | ''tx'' describes a bitcoin transaction, in reply to ''[[#getdata|getdata]]''. When a bloom filter is applied ''tx'' objects are sent automatically for matching transactions following the <code>merkleblock</code>. | ||
Line 511: | Line 625: | ||
| 4 || version || uint32_t || Transaction data format version | | 4 || version || uint32_t || Transaction data format version | ||
|- | |- | ||
| 1+ || tx_in count || [[ | | 0 or 2 || flag || optional uint8_t[2] || If present, always 0001, and indicates the presence of witness data | ||
|- | |||
| 1+ || tx_in count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of Transaction inputs (never zero) | |||
|- | |- | ||
| 41+ || tx_in || tx_in[] || A list of 1 or more transaction inputs or sources for coins | | 41+ || tx_in || tx_in[] || A list of 1 or more transaction inputs or sources for coins | ||
|- | |- | ||
| 1+ || tx_out count || [[ | | 1+ || tx_out count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of Transaction outputs | ||
|- | |- | ||
| 9+ || tx_out || tx_out[] || A list of 1 or more transaction outputs or destinations for coins | | 9+ || tx_out || tx_out[] || A list of 1 or more transaction outputs or destinations for coins | ||
|- | |- | ||
| 4 || lock_time || uint32_t || The block number or timestamp at which this transaction is | | 0+ || tx_witnesses || tx_witness[] || A list of witnesses, one for each input; omitted if ''flag'' is omitted above | ||
|- | |||
| 4 || lock_time || uint32_t || The block number or timestamp at which this transaction is unlocked: | |||
{|class="wikitable" | {|class="wikitable" | ||
! Value !! Description | ! Value !! Description | ||
|- | |- | ||
| 0 || | | 0 || Not locked | ||
|- | |- | ||
| < 500000000 || Block number at which this transaction is | | < 500000000 || Block number at which this transaction is unlocked | ||
|- | |- | ||
| >= 500000000 || UNIX timestamp at which this transaction is | | >= 500000000 || UNIX timestamp at which this transaction is unlocked | ||
|} | |} | ||
If all TxIn inputs have final (0xffffffff) sequence numbers then lock_time is irrelevant. Otherwise, the transaction may not be added to a block until after lock_time (see [[NLockTime]]). | If all TxIn inputs have final (0xffffffff) sequence numbers then lock_time is irrelevant. Otherwise, the transaction may not be added to a block until after lock_time (see [[NLockTime]]). | ||
Line 540: | Line 658: | ||
| 36 || previous_output || outpoint || The previous output transaction reference, as an OutPoint structure | | 36 || previous_output || outpoint || The previous output transaction reference, as an OutPoint structure | ||
|- | |- | ||
| 1+ || script length || [[ | | 1+ || script length || [[Protocol_documentation#Variable_length_integer|var_int]] || The length of the signature script | ||
|- | |- | ||
| ? || signature script || uchar[] || Computational Script for confirming transaction authorization | | ? || signature script || uchar[] || Computational Script for confirming transaction authorization | ||
Line 568: | Line 686: | ||
| 8 || value || int64_t || Transaction Value | | 8 || value || int64_t || Transaction Value | ||
|- | |- | ||
| 1+ || pk_script length || [[ | | 1+ || pk_script length || [[Protocol_documentation#Variable_length_integer|var_int]] || Length of the pk_script | ||
|- | |- | ||
| ? || pk_script || uchar[] || Usually contains the public key as a Bitcoin script setting up conditions to claim this output. | | ? || pk_script || uchar[] || Usually contains the public key as a Bitcoin script setting up conditions to claim this output. | ||
|} | |} | ||
The TxWitness structure consists of a [[Protocol_documentation#Variable_length_integer|var_int]] count of witness data components, followed by (for each witness data component) a [[Protocol_documentation#Variable_length_integer|var_int]] length of the component and the raw component data itself. | |||
Example ''tx'' message: | Example ''tx'' message: | ||
Line 599: | Line 719: | ||
74 78 00 00 00 00 00 00 00 00 00 00 - "tx" command | 74 78 00 00 00 00 00 00 00 00 00 00 - "tx" command | ||
02 01 00 00 - payload is 258 bytes long | 02 01 00 00 - payload is 258 bytes long | ||
E2 93 CD BE - checksum | E2 93 CD BE - payload checksum (internal byte order) | ||
Transaction: | Transaction: | ||
Line 654: | Line 774: | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| 4 || version || | | 4 || version || int32_t || Block version information (note, this is signed) | ||
|- | |- | ||
| 32 || prev_block || char[32] || The hash value of the previous block this particular block references | | 32 || prev_block || char[32] || The hash value of the previous block this particular block references | ||
Line 666: | Line 786: | ||
| 4 || nonce || uint32_t || The nonce used to generate this block… to allow variations of the header and compute different hashes | | 4 || nonce || uint32_t || The nonce used to generate this block… to allow variations of the header and compute different hashes | ||
|- | |- | ||
| | | 1+ || txn_count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of transaction entries | ||
|- | |- | ||
| ? || txns || tx[] || Block transactions, in format of "tx" command | | ? || txns || tx[] || Block transactions, in format of "tx" command | ||
Line 683: | Line 803: | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| | | 1+ || count || [[Protocol_documentation#Variable_length_integer|var_int]] || Number of block headers | ||
|- | |- | ||
| 81x? || headers || [[ | | 81x? || headers || [[Protocol_documentation#Block_Headers|block_header]][] || [[Protocol_documentation#Block_Headers|Block headers]] | ||
|} | |} | ||
Note that the block headers in this packet include a transaction count (a var_int, so there can be more than 81 bytes per header) as opposed to the block headers | Note that the block headers in this packet include a transaction count (a var_int, so there can be more than 81 bytes per header) as opposed to the block headers that are hashed by miners. | ||
=== getaddr === | === getaddr === | ||
Line 702: | Line 822: | ||
No additional data is transmitted with this message. | No additional data is transmitted with this message. | ||
It is specified in [https://github.com/bitcoin/bips/blob/master/bip-0035.mediawiki BIP 35]. Since [https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki BIP 37], only transactions matching the filter are replied. | It is specified in [https://github.com/bitcoin/bips/blob/master/bip-0035.mediawiki BIP 35]. Since [https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki BIP 37], if a [[Protocol_documentation#filterload.2C_filteradd.2C_filterclear.2C_merkleblock|bloom filter]] is loaded, only transactions matching the filter are replied. | ||
=== checkorder === | === checkorder === | ||
Line 755: | Line 875: | ||
|- | |- | ||
| 1+ || reason || var_str || text version of reason for rejection | | 1+ || reason || var_str || text version of reason for rejection | ||
|- | |||
| 0+ || data || char || Optional extra data provided by some errors. Currently, all errors which provide this field fill it with the TXID or block header hash of the object being rejected, so the field is 32 bytes. | |||
|} | |} | ||
Line 778: | Line 900: | ||
| 0x43 || REJECT_CHECKPOINT || | | 0x43 || REJECT_CHECKPOINT || | ||
|} | |} | ||
=== filterload, filteradd, filterclear, merkleblock === | === filterload, filteradd, filterclear, merkleblock === | ||
Line 822: | Line 943: | ||
! Field Size !! Description !! Data type !! Comments | ! Field Size !! Description !! Data type !! Comments | ||
|- | |- | ||
| 4 || version || | | 4 || version || int32_t || Block version information, based upon the software version creating this block (note, this is signed) | ||
|- | |- | ||
| 32 || prev_block || char[32] || The hash value of the previous block this particular block references | | 32 || prev_block || char[32] || The hash value of the previous block this particular block references | ||
Line 836: | Line 957: | ||
| 4 || total_transactions || uint32_t || Number of transactions in the block (including unmatched ones) | | 4 || total_transactions || uint32_t || Number of transactions in the block (including unmatched ones) | ||
|- | |- | ||
| ? || hashes || | | 1+ || hash_count || [[Protocol_documentation#Variable_length_integer|var_int]] || The number of hashes to follow | ||
|- | |||
| 32x? || hashes || char[32] || Hashes in depth-first order | |||
|- | |||
| 1+ || flag_bytes || [[Protocol_documentation#Variable_length_integer|var_int]] || The size of flags (in bytes) to follow | |||
|- | |- | ||
| ? || flags || byte[] || | | ? || flags || byte[] || Flag bits, packed per 8 in a byte, least significant bit first. Extra 0 bits are padded on to reach full byte size. | ||
|} | |} | ||
After a <code>merkleblock</code>, transactions matching the bloom filter are automatically sent in ''[[#tx|tx]]'' messages. | |||
A guide to creating a bloom filter, loading a merkle block, and parsing a partial merkle block tree can be found in the [https://bitcoin.org/en/developer-examples#creating-a-bloom-filter Developer Examples]. | |||
=== alert === | === alert === | ||
An '''alert''' is sent between nodes to send a general notification message throughout the network. If the alert can be confirmed with the signature as having come from | '''Note:''' Support for [[Alert system|alert messages]] has been removed from bitcoin core in March 2016. Read more [https://bitcoin.org/en/alert/2016-11-01-alert-retirement here] | ||
An [[Alert system|'''alert''']] is sent between nodes to send a general notification message throughout the network. If the alert can be confirmed with the signature as having come from the core development group of the Bitcoin software, the message is suggested to be displayed for end-users. Attempts to perform transactions, particularly automated transactions through the client, are suggested to be halted. The text in the Message string should be relayed to log files and any user interfaces. | |||
Alert format: | Alert format: | ||
Line 912: | Line 1,044: | ||
StatusBar: "See bitcoin.org/feb20 if you have trouble connecting after 20 February" | StatusBar: "See bitcoin.org/feb20 if you have trouble connecting after 20 February" | ||
Reserved: <empty> | Reserved: <empty> | ||
=== sendheaders === | |||
Request for Direct headers announcement. | |||
Upon receipt of this message, the node is be permitted, but not required, to announce new blocks by '''headers''' command (instead of '''inv''' command). | |||
This message is supported by the protocol version >= 70012 or Bitcoin Core version >= 0.12.0. | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0130.mediawiki BIP 130] for more information. | |||
No additional data is transmitted with this message. | |||
=== feefilter === | |||
The payload is always 8 bytes long and it encodes 64 bit integer value (LSB / little endian) of '''feerate'''. | |||
The value represents a minimal fee and is expressed in satoshis per 1000 bytes. | |||
Upon receipt of a "feefilter" message, the node will be permitted, but not required, to filter transaction invs for transactions that fall below the feerate provided in the feefilter message interpreted as satoshis per kilobyte. | |||
The fee filter is additive with a bloom filter for transactions so if an SPV client were to load a bloom filter and send a feefilter message, transactions would only be relayed if they passed both filters. | |||
Inv's generated from a mempool message are also subject to a fee filter if it exists. | |||
Feature discovery is enabled by checking protocol version >= 70013 | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0133.mediawiki BIP 133] for more information. | |||
=== sendcmpct === | |||
# The sendcmpct message is defined as a message containing a 1-byte integer followed by a 8-byte integer where pchCommand == "sendcmpct". | |||
# The first integer SHALL be interpreted as a boolean (and MUST have a value of either 1 or 0) | |||
# The second integer SHALL be interpreted as a little-endian version number. Nodes sending a sendcmpct message MUST currently set this value to 1. | |||
# Upon receipt of a "sendcmpct" message with the first and second integers set to 1, the node SHOULD announce new blocks by sending a cmpctblock message. | |||
# Upon receipt of a "sendcmpct" message with the first integer set to 0, the node SHOULD NOT announce new blocks by sending a cmpctblock message, but SHOULD announce new blocks by sending invs or headers, as defined by BIP130. | |||
# Upon receipt of a "sendcmpct" message with the second integer set to something other than 1, nodes MUST treat the peer as if they had not received the message (as it indicates the peer will provide an unexpected encoding in | |||
# cmpctblock, and/or other, messages). This allows future versions to send duplicate sendcmpct messages with different versions as a part of a version handshake for future versions. | |||
# Nodes SHOULD check for a protocol version of >= 70014 before sending sendcmpct messages. | |||
# Nodes MUST NOT send a request for a MSG_CMPCT_BLOCK object to a peer before having received a sendcmpct message from that peer. | |||
This message is only supported by protocol version >= 70014 | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== cmpctblock === | |||
# The cmpctblock message is defined as as a message containing a serialized [[Protocol_documentation#HeaderAndShortIDs|HeaderAndShortIDs]] message and pchCommand == "cmpctblock". | |||
# Upon receipt of a cmpctblock message after sending a sendcmpct message, nodes SHOULD calculate the [[Protocol_documentation#Short_transaction_ID|short transaction ID]] for each unconfirmed transaction they have available (ie in their mempool) and compare each to each short transaction ID in the cmpctblock message. | |||
# After finding already-available transactions, nodes which do not have all transactions available to reconstruct the full block SHOULD request the missing transactions using a getblocktxn message. | |||
# A node MUST NOT send a cmpctblock message unless they are able to respond to a getblocktxn message which requests every transaction in the block. | |||
# A node MUST NOT send a cmpctblock message without having validated that the header properly commits to each transaction in the block, and properly builds on top of the existing chain with a valid proof-of-work. A node MAY send a cmpctblock before validating that each transaction in the block validly spends existing [[UTXO]] set entries. | |||
This message is only supported by protocol version >= 70014 | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== getblocktxn === | |||
# The getblocktxn message is defined as as a message containing a serialized [[Protocol_documentation#BlockTransactionsRequest|BlockTransactionsRequest]] message and pchCommand == "getblocktxn". | |||
# Upon receipt of a properly-formatted getblocktxnmessage, nodes which recently provided the sender of such a message a cmpctblock for the block hash identified in this message MUST respond with an appropriate [[Protocol_documentation#blocktxn|blocktxn]] message. Such a blocktxn message MUST contain exactly and only each transaction which is present in the appropriate block at the index specified in the getblocktxn indexes list, in the order requested. | |||
This message is only supported by protocol version >= 70014 | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
=== blocktxn === | |||
# The blocktxn message is defined as as a message containing a serialized [[Protocol_documentation#BlockTransactions|BlockTransactions]] message and pchCommand == "blocktxn". | |||
# Upon receipt of a properly-formatted requested blocktxn message, nodes SHOULD attempt to reconstruct the full block by: | |||
# Taking the prefilledtxn transactions from the original [[Protocol_documentation#cmpctblock|cmpctblock]] and placing them in the marked positions. | |||
# For each short transaction ID from the original [[Protocol_documentation#cmpctblock|cmpctblock]], in order, find the corresponding transaction either from the blocktxn message or from other sources and place it in the first available position in the block. | |||
# Once the block has been reconstructed, it shall be processed as normal, keeping in mind that short transaction IDs are expected to occasionally collide, and that nodes MUST NOT be penalized for such collisions, wherever they appear. | |||
This message is only supported by protocol version >= 70014 | |||
See [https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki BIP 152] for more information. | |||
== Scripting == | == Scripting == | ||
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[[Category:Technical]] | [[Category:Technical]] | ||
[[Category:Developer]] | [[Category:Developer]] | ||
{{Bitcoin Core documentation}} |
Latest revision as of 18:08, 30 July 2021
This page describes the behavior of the reference client. The Bitcoin protocol is specified by the behavior of the reference client, not by this page. In particular, while this page is quite complete in describing the network protocol, it does not attempt to list all of the rules for block or transaction validity.
Type names used in this documentation are from the C99 standard.
For protocol used in mining, see getblocktemplate.
Common standards
Hashes
Usually, when a hash is computed within bitcoin, it is computed twice. Most of the time SHA-256 hashes are used, however RIPEMD-160 is also used when a shorter hash is desirable (for example when creating a bitcoin address).
Example of double-SHA-256 encoding of string "hello":
hello 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824 (first round of sha-256) 9595c9df90075148eb06860365df33584b75bff782a510c6cd4883a419833d50 (second round of sha-256)
For bitcoin addresses (RIPEMD-160) this would give:
hello 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824 (first round is sha-256) b6a9c8c230722b7c748331a8b450f05566dc7d0f (with ripemd-160)
Merkle Trees
Merkle trees are binary trees of hashes. Merkle trees in bitcoin use a double SHA-256, the SHA-256 hash of the SHA-256 hash of something.
If, when forming a row in the tree (other than the root of the tree), it would have an odd number of elements, the final double-hash is duplicated to ensure that the row has an even number of hashes.
First form the bottom row of the tree with the ordered double-SHA-256 hashes of the byte streams of the transactions in the block.
Then the row above it consists of half that number of hashes. Each entry is the double-SHA-256 of the 64-byte concatenation of the corresponding two hashes below it in the tree.
This procedure repeats recursively until we reach a row consisting of just a single double-hash. This is the Merkle root of the tree.
For example, imagine a block with three transactions a, b and c. The Merkle tree is:
d1 = dhash(a) d2 = dhash(b) d3 = dhash(c) d4 = dhash(c) # a, b, c are 3. that's an odd number, so we take the c twice d5 = dhash(d1 concat d2) d6 = dhash(d3 concat d4) d7 = dhash(d5 concat d6)
where
dhash(a) = sha256(sha256(a))
d7 is the Merkle root of the 3 transactions in this block.
Note: Hashes in Merkle Tree displayed in the Block Explorer are of little-endian notation. For some implementations and calculations, the bytes need to be reversed before they are hashed, and again after the hashing operation.
Signatures
Bitcoin uses Elliptic Curve Digital Signature Algorithm (ECDSA) to sign transactions.
For ECDSA the secp256k1 curve from http://www.secg.org/sec2-v2.pdf is used.
Public keys (in scripts) are given as 04 <x> <y> where x and y are 32 byte big-endian integers representing the coordinates of a point on the curve or in compressed form given as <sign> <x> where <sign> is 0x02 if y is even and 0x03 if y is odd.
Signatures use DER encoding to pack the r and s components into a single byte stream (this is also what OpenSSL produces by default).
Transaction Verification
Transactions are cryptographically signed records that reassign ownership of Bitcoins to new addresses. Transactions have inputs - records which reference the funds from other previous transactions - and outputs - records which determine the new owner of the transferred Bitcoins, and which will be referenced as inputs in future transactions as those funds are respent.
Each input must have a cryptographic digital signature that unlocks the funds from the prior transaction. Only the person possessing the appropriate private key is able to create a satisfactory signature; this in effect ensures that funds can only be spent by their owners.
Each output determines which Bitcoin address (or other criteria, see Script) is the recipient of the funds.
In a transaction, the sum of all inputs must be equal to or greater than the sum of all outputs. If the inputs exceed the outputs, the difference is considered a transaction fee, and is redeemable by whoever first includes the transaction into the block chain.
A special kind of transaction, called a coinbase transaction, has no inputs. It is created by miners, and there is one coinbase transaction per block. Because each block comes with a reward of newly created Bitcoins (e.g. 50 BTC for the first 210,000 blocks), the first transaction of a block is, with few exceptions, the transaction that grants those coins to their recipient (the miner). In addition to the newly created Bitcoins, the coinbase transaction is also used for assigning the recipient of any transaction fees that were paid within the other transactions being included in the same block. The coinbase transaction can assign the entire reward to a single Bitcoin address, or split it in portions among multiple addresses, just like any other transaction. Coinbase transactions always contain outputs totalling the sum of the block reward plus all transaction fees collected from the other transactions in the same block.
The coinbase transaction in block zero cannot be spent. This is due to a quirk of the reference client implementation that would open the potential for a block chain fork if some nodes accepted the spend and others did not[1].
Most Bitcoin outputs encumber the newly transferred coins with a single ECDSA private key. The actual record saved with inputs and outputs isn't necessarily a key, but a script. Bitcoin uses an interpreted scripting system to determine whether an output's criteria have been satisfied, with which more complex operations are possible, such as outputs that require two ECDSA signatures, or two-of-three-signature schemes. An output that references a single Bitcoin address is a typical output; an output actually contains this information in the form of a script that requires a single ECDSA signature (see OP_CHECKSIG). The output script specifies what must be provided to unlock the funds later, and when the time comes in the future to spend the transaction in another input, that input must provide all of the thing(s) that satisfy the requirements defined by the original output script.
Addresses
A bitcoin address is in fact the hash of a ECDSA public key, computed this way:
Version = 1 byte of 0 (zero); on the test network, this is 1 byte of 111 Key hash = Version concatenated with RIPEMD-160(SHA-256(public key)) Checksum = 1st 4 bytes of SHA-256(SHA-256(Key hash)) Bitcoin Address = Base58Encode(Key hash concatenated with Checksum)
The Base58 encoding used is home made, and has some differences. Especially, leading zeroes are kept as single zeroes when conversion happens.
Common structures
Almost all integers are encoded in little endian. Only IP or port number are encoded big endian. All field sizes are numbers of bytes.
Message structure
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | magic | uint32_t | Magic value indicating message origin network, and used to seek to next message when stream state is unknown |
12 | command | char[12] | ASCII string identifying the packet content, NULL padded (non-NULL padding results in packet rejected) |
4 | length | uint32_t | Length of payload in number of bytes |
4 | checksum | uint32_t | First 4 bytes of sha256(sha256(payload)) |
? | payload | uchar[] | The actual data |
Known magic values:
Network | Magic value | Sent over wire as |
---|---|---|
main | 0xD9B4BEF9 | F9 BE B4 D9 |
testnet/regtest | 0xDAB5BFFA | FA BF B5 DA |
testnet3 | 0x0709110B | 0B 11 09 07 |
signet(default) | 0x40CF030A | 0A 03 CF 40 |
namecoin | 0xFEB4BEF9 | F9 BE B4 FE |
Variable length integer
Integer can be encoded depending on the represented value to save space. Variable length integers always precede an array/vector of a type of data that may vary in length. Longer numbers are encoded in little endian.
Value | Storage length | Format |
---|---|---|
< 0xFD | 1 | uint8_t |
<= 0xFFFF | 3 | 0xFD followed by the length as uint16_t |
<= 0xFFFF FFFF | 5 | 0xFE followed by the length as uint32_t |
- | 9 | 0xFF followed by the length as uint64_t |
If you're reading the Satoshi client code (BitcoinQT) it refers to this encoding as a "CompactSize". Modern Bitcoin Core also has the VARINT macro which implements an even more compact integer for the purpose of local storage (which is incompatible with "CompactSize" described here). VARINT is not a part of the protocol.
Variable length string
Variable length string can be stored using a variable length integer followed by the string itself.
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | length | var_int | Length of the string |
? | string | char[] | The string itself (can be empty) |
Network address
When a network address is needed somewhere, this structure is used. Network addresses are not prefixed with a timestamp in the version message.
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | time | uint32 | the Time (version >= 31402). Not present in version message. |
8 | services | uint64_t | same service(s) listed in version |
16 | IPv6/4 | char[16] | IPv6 address. Network byte order. The original client only supported IPv4 and only read the last 4 bytes to get the IPv4 address. However, the IPv4 address is written into the message as a 16 byte IPv4-mapped IPv6 address
(12 bytes 00 00 00 00 00 00 00 00 00 00 FF FF, followed by the 4 bytes of the IPv4 address). |
2 | port | uint16_t | port number, network byte order |
Hexdump example of Network address structure
0000 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 0010 00 00 FF FF 0A 00 00 01 20 8D ........ . Network address: 01 00 00 00 00 00 00 00 - 1 (NODE_NETWORK: see services listed under version command) 00 00 00 00 00 00 00 00 00 00 FF FF 0A 00 00 01 - IPv6: ::ffff:a00:1 or IPv4: 10.0.0.1 20 8D - Port 8333
Inventory Vectors
Inventory vectors are used for notifying other nodes about objects they have or data which is being requested.
Inventory vectors consist of the following data format:
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | type | uint32_t | Identifies the object type linked to this inventory |
32 | hash | char[32] | Hash of the object |
The object type is currently defined as one of the following possibilities:
Value | Name | Description |
---|---|---|
0 | ERROR | Any data of with this number may be ignored |
1 | MSG_TX | Hash is related to a transaction |
2 | MSG_BLOCK | Hash is related to a data block |
3 | MSG_FILTERED_BLOCK | Hash of a block header; identical to MSG_BLOCK. Only to be used in getdata message. Indicates the reply should be a merkleblock message rather than a block message; this only works if a bloom filter has been set. See BIP 37 for more info. |
4 | MSG_CMPCT_BLOCK | Hash of a block header; identical to MSG_BLOCK. Only to be used in getdata message. Indicates the reply should be a cmpctblock message. See BIP 152 for more info. |
0x40000001 | MSG_WITNESS_TX | Hash of a transaction with witness data. See BIP 144 for more info. |
0x40000002 | MSG_WITNESS_BLOCK | Hash of a block with witness data. See BIP 144 for more info. |
0x40000003 | MSG_FILTERED_WITNESS_BLOCK | Hash of a block with witness data. Only to be used in getdata message. Indicates the reply should be a merkleblock message rather than a block message; this only works if a bloom filter has been set. See BIP 144 for more info. |
Other Data Type values are considered reserved for future implementations.
Block Headers
Block headers are sent in a headers packet in response to a getheaders message.
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | version | int32_t | Block version information (note, this is signed) |
32 | prev_block | char[32] | The hash value of the previous block this particular block references |
32 | merkle_root | char[32] | The reference to a Merkle tree collection which is a hash of all transactions related to this block |
4 | timestamp | uint32_t | A timestamp recording when this block was created (Will overflow in 2106[2]) |
4 | bits | uint32_t | The calculated difficulty target being used for this block |
4 | nonce | uint32_t | The nonce used to generate this block… to allow variations of the header and compute different hashes |
1+ | txn_count | var_int | Number of transaction entries, this value is always 0 |
Differential encoding
Several uses of CompactSize below are "differentially encoded". For these, instead of using raw indexes, the number encoded is the difference between the current index and the previous index, minus one. For example, a first index of 0 implies a real index of 0, a second index of 0 thereafter refers to a real index of 1, etc.
PrefilledTransaction
A PrefilledTransaction structure is used in HeaderAndShortIDs to provide a list of a few transactions explicitly.
Field Name | Type | Size | Encoding | Purpose |
---|---|---|---|---|
index | CompactSize | 1, 3 bytes | Compact Size, differentially encoded since the last PrefilledTransaction in a list | The index into the block at which this transaction is |
tx | Transaction | variable | As encoded in tx messages | The transaction which is in the block at index index. |
See BIP 152 for more information.
HeaderAndShortIDs
A HeaderAndShortIDs structure is used to relay a block header, the short transactions IDs used for matching already-available transactions, and a select few transactions which we expect a peer may be missing.
Field Name | Type | Size | Encoding | Purpose |
---|---|---|---|---|
header | Block header | 80 bytes | First 80 bytes of the block as defined by the encoding used by "block" messages | The header of the block being provided |
nonce | uint64_t | 8 bytes | Little Endian | A nonce for use in short transaction ID calculations |
shortids_length | CompactSize | 1 or 3 bytes | As used to encode array lengths elsewhere | The number of short transaction IDs in shortids (ie block tx count - prefilledtxn_length) |
shortids | List of 6-byte integers | 6*shortids_length bytes | Little Endian | The short transaction IDs calculated from the transactions which were not provided explicitly in prefilledtxn |
prefilledtxn_length | CompactSize | 1 or 3 bytes | As used to encode array lengths elsewhere | The number of prefilled transactions in prefilledtxn (ie block tx count - shortids_length) |
prefilledtxn | List of PrefilledTransactions | variable size*prefilledtxn_length | As defined by PrefilledTransaction definition, above | Used to provide the coinbase transaction and a select few which we expect a peer may be missing |
See BIP 152 for more information.
BlockTransactionsRequest
A BlockTransactionsRequest structure is used to list transaction indexes in a block being requested.
Field Name | Type | Size | Encoding | Purpose |
---|---|---|---|---|
blockhash | Binary blob | 32 bytes | The output from a double-SHA256 of the block header, as used elsewhere | The blockhash of the block which the transactions being requested are in |
indexes_length | CompactSize | 1 or 3 bytes | As used to encode array lengths elsewhere | The number of transactions being requested |
indexes | List of CompactSizes | 1 or 3 bytes*indexes_length | Differentially encoded | The indexes of the transactions being requested in the block |
See BIP 152 for more information.
BlockTransactions
A BlockTransactions structure is used to provide some of the transactions in a block, as requested.
Field Name | Type | Size | Encoding | Purpose |
---|---|---|---|---|
blockhash | Binary blob | 32 bytes | The output from a double-SHA256 of the block header, as used elsewhere | The blockhash of the block which the transactions being provided are in |
transactions_length | CompactSize | 1 or 3 bytes | As used to encode array lengths elsewhere | The number of transactions provided |
transactions | List of Transactions | variable | As encoded in tx messages | The transactions provided |
See BIP 152 for more information.
Short transaction ID
Short transaction IDs are used to represent a transaction without sending a full 256-bit hash. They are calculated by:
- single-SHA256 hashing the block header with the nonce appended (in little-endian)
- Running SipHash-2-4 with the input being the transaction ID and the keys (k0/k1) set to the first two little-endian 64-bit integers from the above hash, respectively.
- Dropping the 2 most significant bytes from the SipHash output to make it 6 bytes.
See BIP 152 for more information.
Message types
version
When a node creates an outgoing connection, it will immediately advertise its version. The remote node will respond with its version. No further communication is possible until both peers have exchanged their version.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | version | int32_t | Identifies protocol version being used by the node |
8 | services | uint64_t | bitfield of features to be enabled for this connection |
8 | timestamp | int64_t | standard UNIX timestamp in seconds |
26 | addr_recv | net_addr | The network address of the node receiving this message |
Fields below require version ≥ 106 | |||
26 | addr_from | net_addr | Field can be ignored. This used to be the network address of the node emitting this message, but most P2P implementations send 26 dummy bytes. The "services" field of the address would also be redundant with the second field of the version message. |
8 | nonce | uint64_t | Node random nonce, randomly generated every time a version packet is sent. This nonce is used to detect connections to self. |
? | user_agent | var_str | User Agent (0x00 if string is 0 bytes long) |
4 | start_height | int32_t | The last block received by the emitting node |
Fields below require version ≥ 70001 | |||
1 | relay | bool | Whether the remote peer should announce relayed transactions or not, see BIP 0037 |
A "verack" packet shall be sent if the version packet was accepted.
The following services are currently assigned:
Value | Name | Description |
---|---|---|
1 | NODE_NETWORK | This node can be asked for full blocks instead of just headers. |
2 | NODE_GETUTXO | See BIP 0064 |
4 | NODE_BLOOM | See BIP 0111 |
8 | NODE_WITNESS | See BIP 0144 |
16 | NODE_XTHIN | Never formally proposed (as a BIP), and discontinued. Was historically sporadically seen on the network. |
64 | NODE_COMPACT_FILTERS | See BIP 0157 |
1024 | NODE_NETWORK_LIMITED | See BIP 0159 |
Hexdump example of version message (OBSOLETE EXAMPLE: This example lacks a checksum and user-agent):
0000 F9 BE B4 D9 76 65 72 73 69 6F 6E 00 00 00 00 00 ....version..... 0010 55 00 00 00 9C 7C 00 00 01 00 00 00 00 00 00 00 U....|.......... 0020 E6 15 10 4D 00 00 00 00 01 00 00 00 00 00 00 00 ...M............ 0030 00 00 00 00 00 00 00 00 00 00 FF FF 0A 00 00 01 ................ 0040 20 8D 01 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 0050 00 00 00 00 FF FF 0A 00 00 02 20 8D DD 9D 20 2C .......... ... , 0060 3A B4 57 13 00 55 81 01 00 :.W..U... Message header: F9 BE B4 D9 - Main network magic bytes 76 65 72 73 69 6F 6E 00 00 00 00 00 - "version" command 55 00 00 00 - Payload is 85 bytes long - No checksum in version message until 20 February 2012. See https://bitcointalk.org/index.php?topic=55852.0 Version message: 9C 7C 00 00 - 31900 (version 0.3.19) 01 00 00 00 00 00 00 00 - 1 (NODE_NETWORK services) E6 15 10 4D 00 00 00 00 - Mon Dec 20 21:50:14 EST 2010 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF FF 0A 00 00 01 20 8D - Recipient address info - see Network Address 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF FF 0A 00 00 02 20 8D - Sender address info - see Network Address DD 9D 20 2C 3A B4 57 13 - Node random unique ID 00 - "" sub-version string (string is 0 bytes long) 55 81 01 00 - Last block sending node has is block #98645
And here's a modern (60002) protocol version client advertising itself to a local peer...
Newer protocol includes the checksum now, this is from a mainline (satoshi) client during an outgoing connection to another local client, notice that it does not fill out the address information at all when the source or destination is "unroutable".
0000 f9 be b4 d9 76 65 72 73 69 6f 6e 00 00 00 00 00 ....version..... 0010 64 00 00 00 35 8d 49 32 62 ea 00 00 01 00 00 00 d...5.I2b....... 0020 00 00 00 00 11 b2 d0 50 00 00 00 00 01 00 00 00 .......P........ 0030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ................ 0040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 0050 00 00 00 00 00 00 00 00 ff ff 00 00 00 00 00 00 ................ 0060 3b 2e b3 5d 8c e6 17 65 0f 2f 53 61 74 6f 73 68 ;..]...e./Satosh 0070 69 3a 30 2e 37 2e 32 2f c0 3e 03 00 i:0.7.2/.>.. Message Header: F9 BE B4 D9 - Main network magic bytes 76 65 72 73 69 6F 6E 00 00 00 00 00 - "version" command 64 00 00 00 - Payload is 100 bytes long 35 8d 49 32 - payload checksum (internal byte order) Version message: 62 EA 00 00 - 60002 (protocol version 60002) 01 00 00 00 00 00 00 00 - 1 (NODE_NETWORK services) 11 B2 D0 50 00 00 00 00 - Tue Dec 18 10:12:33 PST 2012 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF FF 00 00 00 00 00 00 - Recipient address info - see Network Address 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF FF 00 00 00 00 00 00 - Sender address info - see Network Address 3B 2E B3 5D 8C E6 17 65 - Node ID 0F 2F 53 61 74 6F 73 68 69 3A 30 2E 37 2E 32 2F - "/Satoshi:0.7.2/" sub-version string (string is 15 bytes long) C0 3E 03 00 - Last block sending node has is block #212672
verack
The verack message is sent in reply to version. This message consists of only a message header with the command string "verack".
Hexdump of the verack message:
0000 F9 BE B4 D9 76 65 72 61 63 6B 00 00 00 00 00 00 ....verack...... 0010 00 00 00 00 5D F6 E0 E2 ........ Message header: F9 BE B4 D9 - Main network magic bytes 76 65 72 61 63 6B 00 00 00 00 00 00 - "verack" command 00 00 00 00 - Payload is 0 bytes long 5D F6 E0 E2 - Checksum (internal byte order)
addr
Provide information on known nodes of the network. Non-advertised nodes should be forgotten after typically 3 hours
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | count | var_int | Number of address entries (max: 1000) |
30x? | addr_list | (uint32_t + net_addr)[] | Address of other nodes on the network. version < 209 will only read the first one. The uint32_t is a timestamp (see note below). |
Note: Starting version 31402, addresses are prefixed with a timestamp. If no timestamp is present, the addresses should not be relayed to other peers, unless it is indeed confirmed they are up.
Hexdump example of addr message:
0000 F9 BE B4 D9 61 64 64 72 00 00 00 00 00 00 00 00 ....addr........ 0010 1F 00 00 00 ED 52 39 9B 01 E2 15 10 4D 01 00 00 .....R9.....M... 0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF ................ 0030 FF 0A 00 00 01 20 8D ..... . Message Header: F9 BE B4 D9 - Main network magic bytes 61 64 64 72 00 00 00 00 00 00 00 00 - "addr" 1F 00 00 00 - payload is 31 bytes long ED 52 39 9B - payload checksum (internal byte order) Payload: 01 - 1 address in this message Address: E2 15 10 4D - Mon Dec 20 21:50:10 EST 2010 (only when version is >= 31402) 01 00 00 00 00 00 00 00 - 1 (NODE_NETWORK service - see version message) 00 00 00 00 00 00 00 00 00 00 FF FF 0A 00 00 01 - IPv4: 10.0.0.1, IPv6: ::ffff:10.0.0.1 (IPv4-mapped IPv6 address) 20 8D - port 8333
inv
Allows a node to advertise its knowledge of one or more objects. It can be received unsolicited, or in reply to getblocks.
Payload (maximum 50,000 entries, which is just over 1.8 megabytes):
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | count | var_int | Number of inventory entries |
36x? | inventory | inv_vect[] | Inventory vectors |
getdata
getdata is used in response to inv, to retrieve the content of a specific object, and is usually sent after receiving an inv packet, after filtering known elements. It can be used to retrieve transactions, but only if they are in the memory pool or relay set - arbitrary access to transactions in the chain is not allowed to avoid having clients start to depend on nodes having full transaction indexes (which modern nodes do not).
Payload (maximum 50,000 entries, which is just over 1.8 megabytes):
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | count | var_int | Number of inventory entries |
36x? | inventory | inv_vect[] | Inventory vectors |
notfound
notfound is a response to a getdata, sent if any requested data items could not be relayed, for example, because the requested transaction was not in the memory pool or relay set.
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | count | var_int | Number of inventory entries |
36x? | inventory | inv_vect[] | Inventory vectors |
getblocks
Return an inv packet containing the list of blocks starting right after the last known hash in the block locator object, up to hash_stop or 500 blocks, whichever comes first.
The locator hashes are processed by a node in the order as they appear in the message. If a block hash is found in the node's main chain, the list of its children is returned back via the inv message and the remaining locators are ignored, no matter if the requested limit was reached, or not.
To receive the next blocks hashes, one needs to issue getblocks again with a new block locator object. Keep in mind that some clients may provide blocks which are invalid if the block locator object contains a hash on the invalid branch.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | version | uint32_t | the protocol version |
1+ | hash count | var_int | number of block locator hash entries |
32+ | block locator hashes | char[32] | block locator object; newest back to genesis block (dense to start, but then sparse) |
32 | hash_stop | char[32] | hash of the last desired block; set to zero to get as many blocks as possible (500) |
To create the block locator hashes, keep pushing hashes until you go back to the genesis block. After pushing 10 hashes back, the step backwards doubles every loop:
// From libbitcoin which is under AGPL std::vector<size_t> block_locator_indexes(size_t top_height) { std::vector<size_t> indexes; // Modify the step in the iteration. int64_t step = 1; // Start at the top of the chain and work backwards. for (auto index = (int64_t)top_height; index > 0; index -= step) { // Push top 10 indexes first, then back off exponentially. if (indexes.size() >= 10) step *= 2; indexes.push_back((size_t)index); } // Push the genesis block index. indexes.push_back(0); return indexes; }
Note that it is allowed to send in fewer known hashes down to a minimum of just one hash. However, the purpose of the block locator object is to detect a wrong branch in the caller's main chain. If the peer detects that you are off the main chain, it will send in block hashes which are earlier than your last known block. So if you just send in your last known hash and it is off the main chain, the peer starts over at block #1.
getheaders
Return a headers packet containing the headers of blocks starting right after the last known hash in the block locator object, up to hash_stop or 2000 blocks, whichever comes first. To receive the next block headers, one needs to issue getheaders again with a new block locator object. Keep in mind that some clients may provide headers of blocks which are invalid if the block locator object contains a hash on the invalid branch.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | version | uint32_t | the protocol version |
1+ | hash count | var_int | number of block locator hash entries |
32+ | block locator hashes | char[32] | block locator object; newest back to genesis block (dense to start, but then sparse) |
32 | hash_stop | char[32] | hash of the last desired block header; set to zero to get as many blocks as possible (2000) |
For the block locator object in this packet, the same rules apply as for the getblocks packet.
tx
tx describes a bitcoin transaction, in reply to getdata. When a bloom filter is applied tx objects are sent automatically for matching transactions following the merkleblock
.
Field Size | Description | Data type | Comments | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
4 | version | uint32_t | Transaction data format version | ||||||||
0 or 2 | flag | optional uint8_t[2] | If present, always 0001, and indicates the presence of witness data | ||||||||
1+ | tx_in count | var_int | Number of Transaction inputs (never zero) | ||||||||
41+ | tx_in | tx_in[] | A list of 1 or more transaction inputs or sources for coins | ||||||||
1+ | tx_out count | var_int | Number of Transaction outputs | ||||||||
9+ | tx_out | tx_out[] | A list of 1 or more transaction outputs or destinations for coins | ||||||||
0+ | tx_witnesses | tx_witness[] | A list of witnesses, one for each input; omitted if flag is omitted above | ||||||||
4 | lock_time | uint32_t | The block number or timestamp at which this transaction is unlocked:
If all TxIn inputs have final (0xffffffff) sequence numbers then lock_time is irrelevant. Otherwise, the transaction may not be added to a block until after lock_time (see NLockTime). |
TxIn consists of the following fields:
Field Size | Description | Data type | Comments |
---|---|---|---|
36 | previous_output | outpoint | The previous output transaction reference, as an OutPoint structure |
1+ | script length | var_int | The length of the signature script |
? | signature script | uchar[] | Computational Script for confirming transaction authorization |
4 | sequence | uint32_t | Transaction version as defined by the sender. Intended for "replacement" of transactions when information is updated before inclusion into a block. |
The OutPoint structure consists of the following fields:
Field Size | Description | Data type | Comments |
---|---|---|---|
32 | hash | char[32] | The hash of the referenced transaction. |
4 | index | uint32_t | The index of the specific output in the transaction. The first output is 0, etc. |
The Script structure consists of a series of pieces of information and operations related to the value of the transaction.
(Structure to be expanded in the future… see script.h and script.cpp and Script for more information)
The TxOut structure consists of the following fields:
Field Size | Description | Data type | Comments |
---|---|---|---|
8 | value | int64_t | Transaction Value |
1+ | pk_script length | var_int | Length of the pk_script |
? | pk_script | uchar[] | Usually contains the public key as a Bitcoin script setting up conditions to claim this output. |
The TxWitness structure consists of a var_int count of witness data components, followed by (for each witness data component) a var_int length of the component and the raw component data itself.
Example tx message:
000000 F9 BE B4 D9 74 78 00 00 00 00 00 00 00 00 00 00 ....tx.......... 000010 02 01 00 00 E2 93 CD BE 01 00 00 00 01 6D BD DB .............m.. 000020 08 5B 1D 8A F7 51 84 F0 BC 01 FA D5 8D 12 66 E9 .[...Q........f. 000030 B6 3B 50 88 19 90 E4 B4 0D 6A EE 36 29 00 00 00 .;P......j.6)... 000040 00 8B 48 30 45 02 21 00 F3 58 1E 19 72 AE 8A C7 ..H0E.!..X..r... 000050 C7 36 7A 7A 25 3B C1 13 52 23 AD B9 A4 68 BB 3A .6zz%;..R#...h.: 000060 59 23 3F 45 BC 57 83 80 02 20 59 AF 01 CA 17 D0 Y#?E.W... Y..... 000070 0E 41 83 7A 1D 58 E9 7A A3 1B AE 58 4E DE C2 8D .A.z.X.z...XN... 000080 35 BD 96 92 36 90 91 3B AE 9A 01 41 04 9C 02 BF 5...6..;...A.... 000090 C9 7E F2 36 CE 6D 8F E5 D9 40 13 C7 21 E9 15 98 .~.6.m...@..!... 0000A0 2A CD 2B 12 B6 5D 9B 7D 59 E2 0A 84 20 05 F8 FC *.+..].}Y... ... 0000B0 4E 02 53 2E 87 3D 37 B9 6F 09 D6 D4 51 1A DA 8F N.S..=7.o...Q... 0000C0 14 04 2F 46 61 4A 4C 70 C0 F1 4B EF F5 FF FF FF ../FaJLp..K..... 0000D0 FF 02 40 4B 4C 00 00 00 00 00 19 76 A9 14 1A A0 ..@KL......v.... 0000E0 CD 1C BE A6 E7 45 8A 7A BA D5 12 A9 D9 EA 1A FB .....E.z........ 0000F0 22 5E 88 AC 80 FA E9 C7 00 00 00 00 19 76 A9 14 "^...........v.. 000100 0E AB 5B EA 43 6A 04 84 CF AB 12 48 5E FD A0 B7 ..[.Cj.....H^... 000110 8B 4E CC 52 88 AC 00 00 00 00 .N.R...... Message header: F9 BE B4 D9 - main network magic bytes 74 78 00 00 00 00 00 00 00 00 00 00 - "tx" command 02 01 00 00 - payload is 258 bytes long E2 93 CD BE - payload checksum (internal byte order) Transaction: 01 00 00 00 - version Inputs: 01 - number of transaction inputs Input 1: 6D BD DB 08 5B 1D 8A F7 51 84 F0 BC 01 FA D5 8D - previous output (outpoint) 12 66 E9 B6 3B 50 88 19 90 E4 B4 0D 6A EE 36 29 00 00 00 00 8B - script is 139 bytes long 48 30 45 02 21 00 F3 58 1E 19 72 AE 8A C7 C7 36 - signature script (scriptSig) 7A 7A 25 3B C1 13 52 23 AD B9 A4 68 BB 3A 59 23 3F 45 BC 57 83 80 02 20 59 AF 01 CA 17 D0 0E 41 83 7A 1D 58 E9 7A A3 1B AE 58 4E DE C2 8D 35 BD 96 92 36 90 91 3B AE 9A 01 41 04 9C 02 BF C9 7E F2 36 CE 6D 8F E5 D9 40 13 C7 21 E9 15 98 2A CD 2B 12 B6 5D 9B 7D 59 E2 0A 84 20 05 F8 FC 4E 02 53 2E 87 3D 37 B9 6F 09 D6 D4 51 1A DA 8F 14 04 2F 46 61 4A 4C 70 C0 F1 4B EF F5 FF FF FF FF - sequence Outputs: 02 - 2 Output Transactions Output 1: 40 4B 4C 00 00 00 00 00 - 0.05 BTC (5000000) 19 - pk_script is 25 bytes long 76 A9 14 1A A0 CD 1C BE A6 E7 45 8A 7A BA D5 12 - pk_script A9 D9 EA 1A FB 22 5E 88 AC Output 2: 80 FA E9 C7 00 00 00 00 - 33.54 BTC (3354000000) 19 - pk_script is 25 bytes long 76 A9 14 0E AB 5B EA 43 6A 04 84 CF AB 12 48 5E - pk_script FD A0 B7 8B 4E CC 52 88 AC Locktime: 00 00 00 00 - lock time
block
The block message is sent in response to a getdata message which requests transaction information from a block hash.
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | version | int32_t | Block version information (note, this is signed) |
32 | prev_block | char[32] | The hash value of the previous block this particular block references |
32 | merkle_root | char[32] | The reference to a Merkle tree collection which is a hash of all transactions related to this block |
4 | timestamp | uint32_t | A Unix timestamp recording when this block was created (Currently limited to dates before the year 2106!) |
4 | bits | uint32_t | The calculated difficulty target being used for this block |
4 | nonce | uint32_t | The nonce used to generate this block… to allow variations of the header and compute different hashes |
1+ | txn_count | var_int | Number of transaction entries |
? | txns | tx[] | Block transactions, in format of "tx" command |
The SHA256 hash that identifies each block (and which must have a run of 0 bits) is calculated from the first 6 fields of this structure (version, prev_block, merkle_root, timestamp, bits, nonce, and standard SHA256 padding, making two 64-byte chunks in all) and not from the complete block. To calculate the hash, only two chunks need to be processed by the SHA256 algorithm. Since the nonce field is in the second chunk, the first chunk stays constant during mining and therefore only the second chunk needs to be processed. However, a Bitcoin hash is the hash of the hash, so two SHA256 rounds are needed for each mining iteration. See Block hashing algorithm for details and an example.
headers
The headers packet returns block headers in response to a getheaders packet.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | count | var_int | Number of block headers |
81x? | headers | block_header[] | Block headers |
Note that the block headers in this packet include a transaction count (a var_int, so there can be more than 81 bytes per header) as opposed to the block headers that are hashed by miners.
getaddr
The getaddr message sends a request to a node asking for information about known active peers to help with finding potential nodes in the network. The response to receiving this message is to transmit one or more addr messages with one or more peers from a database of known active peers. The typical presumption is that a node is likely to be active if it has been sending a message within the last three hours.
No additional data is transmitted with this message.
mempool
The mempool message sends a request to a node asking for information about transactions it has verified but which have not yet confirmed. The response to receiving this message is an inv message containing the transaction hashes for all the transactions in the node's mempool.
No additional data is transmitted with this message.
It is specified in BIP 35. Since BIP 37, if a bloom filter is loaded, only transactions matching the filter are replied.
checkorder
This message was used for IP Transactions. As IP transactions have been deprecated, it is no longer used.
submitorder
This message was used for IP Transactions. As IP transactions have been deprecated, it is no longer used.
reply
This message was used for IP Transactions. As IP transactions have been deprecated, it is no longer used.
ping
The ping message is sent primarily to confirm that the TCP/IP connection is still valid. An error in transmission is presumed to be a closed connection and the address is removed as a current peer.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
8 | nonce | uint64_t | random nonce |
pong
The pong message is sent in response to a ping message. In modern protocol versions, a pong response is generated using a nonce included in the ping.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
8 | nonce | uint64_t | nonce from ping |
reject
The reject message is sent when messages are rejected.
Payload:
Field Size | Description | Data type | Comments |
---|---|---|---|
1+ | message | var_str | type of message rejected |
1 | ccode | char | code relating to rejected message |
1+ | reason | var_str | text version of reason for rejection |
0+ | data | char | Optional extra data provided by some errors. Currently, all errors which provide this field fill it with the TXID or block header hash of the object being rejected, so the field is 32 bytes. |
CCodes
Value | Name | Description |
---|---|---|
0x01 | REJECT_MALFORMED | |
0x10 | REJECT_INVALID | |
0x11 | REJECT_OBSOLETE | |
0x12 | REJECT_DUPLICATE | |
0x40 | REJECT_NONSTANDARD | |
0x41 | REJECT_DUST | |
0x42 | REJECT_INSUFFICIENTFEE | |
0x43 | REJECT_CHECKPOINT |
filterload, filteradd, filterclear, merkleblock
These messages are related to Bloom filtering of connections and are defined in BIP 0037.
The filterload
command is defined as follows:
Field Size | Description | Data type | Comments |
---|---|---|---|
? | filter | uint8_t[] | The filter itself is simply a bit field of arbitrary byte-aligned size. The maximum size is 36,000 bytes. |
4 | nHashFuncs | uint32_t | The number of hash functions to use in this filter. The maximum value allowed in this field is 50. |
4 | nTweak | uint32_t | A random value to add to the seed value in the hash function used by the bloom filter. |
1 | nFlags | uint8_t | A set of flags that control how matched items are added to the filter. |
See below for a description of the Bloom filter algorithm and how to select nHashFuncs and filter size for a desired false positive rate.
Upon receiving a filterload
command, the remote peer will immediately restrict the broadcast transactions it announces (in inv packets) to transactions matching the filter, where the matching algorithm is specified below. The flags control the update behaviour of the matching algorithm.
The filteradd
command is defined as follows:
Field Size | Description | Data type | Comments |
---|---|---|---|
? | data | uint8_t[] | The data element to add to the current filter. |
The data field must be smaller than or equal to 520 bytes in size (the maximum size of any potentially matched object).
The given data element will be added to the Bloom filter. A filter must have been previously provided using filterload
. This command is useful if a new key or script is added to a clients wallet whilst it has connections to the network open, it avoids the need to re-calculate and send an entirely new filter to every peer (though doing so is usually advisable to maintain anonymity).
The filterclear
command has no arguments at all.
After a filter has been set, nodes don't merely stop announcing non-matching transactions, they can also serve filtered blocks. A filtered block is defined by the merkleblock
message and is defined like this:
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | version | int32_t | Block version information, based upon the software version creating this block (note, this is signed) |
32 | prev_block | char[32] | The hash value of the previous block this particular block references |
32 | merkle_root | char[32] | The reference to a Merkle tree collection which is a hash of all transactions related to this block |
4 | timestamp | uint32_t | A timestamp recording when this block was created (Limited to 2106!) |
4 | bits | uint32_t | The calculated difficulty target being used for this block |
4 | nonce | uint32_t | The nonce used to generate this block… to allow variations of the header and compute different hashes |
4 | total_transactions | uint32_t | Number of transactions in the block (including unmatched ones) |
1+ | hash_count | var_int | The number of hashes to follow |
32x? | hashes | char[32] | Hashes in depth-first order |
1+ | flag_bytes | var_int | The size of flags (in bytes) to follow |
? | flags | byte[] | Flag bits, packed per 8 in a byte, least significant bit first. Extra 0 bits are padded on to reach full byte size. |
After a merkleblock
, transactions matching the bloom filter are automatically sent in tx messages.
A guide to creating a bloom filter, loading a merkle block, and parsing a partial merkle block tree can be found in the Developer Examples.
alert
Note: Support for alert messages has been removed from bitcoin core in March 2016. Read more here
An alert is sent between nodes to send a general notification message throughout the network. If the alert can be confirmed with the signature as having come from the core development group of the Bitcoin software, the message is suggested to be displayed for end-users. Attempts to perform transactions, particularly automated transactions through the client, are suggested to be halted. The text in the Message string should be relayed to log files and any user interfaces.
Alert format:
Field Size | Description | Data type | Comments |
---|---|---|---|
? | payload | uchar[] | Serialized alert payload |
? | signature | uchar[] | An ECDSA signature of the message |
The developers of Satoshi's client use this public key for signing alerts:
04fc9702847840aaf195de8442ebecedf5b095cdbb9bc716bda9110971b28a49e0ead8564ff0db22209e0374782c093bb899692d524e9d6a6956e7c5ecbcd68284 (hash) 1AGRxqDa5WjUKBwHB9XYEjmkv1ucoUUy1s
The payload is serialized into a uchar[] to ensure that versions using incompatible alert formats can still relay alerts among one another. The current alert payload format is:
Field Size | Description | Data type | Comments |
---|---|---|---|
4 | Version | int32_t | Alert format version |
8 | RelayUntil | int64_t | The timestamp beyond which nodes should stop relaying this alert |
8 | Expiration | int64_t | The timestamp beyond which this alert is no longer in effect and should be ignored |
4 | ID | int32_t | A unique ID number for this alert |
4 | Cancel | int32_t | All alerts with an ID number less than or equal to this number should be cancelled: deleted and not accepted in the future |
? | setCancel | set<int32_t> | All alert IDs contained in this set should be cancelled as above |
4 | MinVer | int32_t | This alert only applies to versions greater than or equal to this version. Other versions should still relay it. |
4 | MaxVer | int32_t | This alert only applies to versions less than or equal to this version. Other versions should still relay it. |
? | setSubVer | set<string> | If this set contains any elements, then only nodes that have their subVer contained in this set are affected by the alert. Other versions should still relay it. |
4 | Priority | int32_t | Relative priority compared to other alerts |
? | Comment | string | A comment on the alert that is not displayed |
? | StatusBar | string | The alert message that is displayed to the user |
? | Reserved | string | Reserved |
Note: set<type> in the table above is a variable length integer followed by the number of fields of the given type (either int32_t or variable length string)
Sample alert (no message header):
73010000003766404f00000000b305434f00000000f2030000f1030000001027000048ee0000 0064000000004653656520626974636f696e2e6f72672f666562323020696620796f75206861 76652074726f75626c6520636f6e6e656374696e672061667465722032302046656272756172 79004730450221008389df45f0703f39ec8c1cc42c13810ffcae14995bb648340219e353b63b 53eb022009ec65e1c1aaeec1fd334c6b684bde2b3f573060d5b70c3a46723326e4e8a4f1 Version: 1 RelayUntil: 1329620535 Expiration: 1329792435 ID: 1010 Cancel: 1009 setCancel: <empty> MinVer: 10000 MaxVer: 61000 setSubVer: <empty> Priority: 100 Comment: <empty> StatusBar: "See bitcoin.org/feb20 if you have trouble connecting after 20 February" Reserved: <empty>
sendheaders
Request for Direct headers announcement.
Upon receipt of this message, the node is be permitted, but not required, to announce new blocks by headers command (instead of inv command).
This message is supported by the protocol version >= 70012 or Bitcoin Core version >= 0.12.0.
See BIP 130 for more information.
No additional data is transmitted with this message.
feefilter
The payload is always 8 bytes long and it encodes 64 bit integer value (LSB / little endian) of feerate. The value represents a minimal fee and is expressed in satoshis per 1000 bytes.
Upon receipt of a "feefilter" message, the node will be permitted, but not required, to filter transaction invs for transactions that fall below the feerate provided in the feefilter message interpreted as satoshis per kilobyte.
The fee filter is additive with a bloom filter for transactions so if an SPV client were to load a bloom filter and send a feefilter message, transactions would only be relayed if they passed both filters.
Inv's generated from a mempool message are also subject to a fee filter if it exists.
Feature discovery is enabled by checking protocol version >= 70013
See BIP 133 for more information.
sendcmpct
- The sendcmpct message is defined as a message containing a 1-byte integer followed by a 8-byte integer where pchCommand == "sendcmpct".
- The first integer SHALL be interpreted as a boolean (and MUST have a value of either 1 or 0)
- The second integer SHALL be interpreted as a little-endian version number. Nodes sending a sendcmpct message MUST currently set this value to 1.
- Upon receipt of a "sendcmpct" message with the first and second integers set to 1, the node SHOULD announce new blocks by sending a cmpctblock message.
- Upon receipt of a "sendcmpct" message with the first integer set to 0, the node SHOULD NOT announce new blocks by sending a cmpctblock message, but SHOULD announce new blocks by sending invs or headers, as defined by BIP130.
- Upon receipt of a "sendcmpct" message with the second integer set to something other than 1, nodes MUST treat the peer as if they had not received the message (as it indicates the peer will provide an unexpected encoding in
- cmpctblock, and/or other, messages). This allows future versions to send duplicate sendcmpct messages with different versions as a part of a version handshake for future versions.
- Nodes SHOULD check for a protocol version of >= 70014 before sending sendcmpct messages.
- Nodes MUST NOT send a request for a MSG_CMPCT_BLOCK object to a peer before having received a sendcmpct message from that peer.
This message is only supported by protocol version >= 70014
See BIP 152 for more information.
cmpctblock
- The cmpctblock message is defined as as a message containing a serialized HeaderAndShortIDs message and pchCommand == "cmpctblock".
- Upon receipt of a cmpctblock message after sending a sendcmpct message, nodes SHOULD calculate the short transaction ID for each unconfirmed transaction they have available (ie in their mempool) and compare each to each short transaction ID in the cmpctblock message.
- After finding already-available transactions, nodes which do not have all transactions available to reconstruct the full block SHOULD request the missing transactions using a getblocktxn message.
- A node MUST NOT send a cmpctblock message unless they are able to respond to a getblocktxn message which requests every transaction in the block.
- A node MUST NOT send a cmpctblock message without having validated that the header properly commits to each transaction in the block, and properly builds on top of the existing chain with a valid proof-of-work. A node MAY send a cmpctblock before validating that each transaction in the block validly spends existing UTXO set entries.
This message is only supported by protocol version >= 70014
See BIP 152 for more information.
getblocktxn
- The getblocktxn message is defined as as a message containing a serialized BlockTransactionsRequest message and pchCommand == "getblocktxn".
- Upon receipt of a properly-formatted getblocktxnmessage, nodes which recently provided the sender of such a message a cmpctblock for the block hash identified in this message MUST respond with an appropriate blocktxn message. Such a blocktxn message MUST contain exactly and only each transaction which is present in the appropriate block at the index specified in the getblocktxn indexes list, in the order requested.
This message is only supported by protocol version >= 70014
See BIP 152 for more information.
blocktxn
- The blocktxn message is defined as as a message containing a serialized BlockTransactions message and pchCommand == "blocktxn".
- Upon receipt of a properly-formatted requested blocktxn message, nodes SHOULD attempt to reconstruct the full block by:
- Taking the prefilledtxn transactions from the original cmpctblock and placing them in the marked positions.
- For each short transaction ID from the original cmpctblock, in order, find the corresponding transaction either from the blocktxn message or from other sources and place it in the first available position in the block.
- Once the block has been reconstructed, it shall be processed as normal, keeping in mind that short transaction IDs are expected to occasionally collide, and that nodes MUST NOT be penalized for such collisions, wherever they appear.
This message is only supported by protocol version >= 70014
See BIP 152 for more information.
Scripting
See script.
See Also
- Network
- Protocol rules
- Hardfork Wishlist
- Developer Documentation on bitcoin.org
- Bitcoin dissectors for Wireshark: https://github.com/lbotsch/wireshark-bitcoin https://github.com/op-sig/bitcoin-wireshark-dissector
References
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